1. Field of the Invention
The present invention relates to a piezoelectric actuator in which at least one-directional movement of a moving body is facilitated, and which can insure high movement conversion efficiency even when miniaturized.
2. Background Information
FIG. 7 is a perspective drawing showing an example of a piezoelectric actuator of the related art. This piezoelectric actuator 300 is used as an XY stage for movement over a microscopic distance, and movement in each axial direction is realized by stacked piezoelectric elements. A metal plate is punched by wire discharge or die processing on an anchor block and a movable table 303 is placed inside the punched out part 302. Respective support springs 304 are formed on the four edges of the movable table 303 and guide sections 305 are attached to the four edges of the movable table 303 through the support springs 304. Also, stacked piezoelectric elements 306 are attached to ends of the guide sections at right angles to the movable table 306.
An enlarged plan view of a support spring 304 is shown in FIG. 8. This support spring 304 is formed as a rectangular frame, and a long edge 304a is thin while a short edge 304b is thick. This is because by making the long edge 304a long and thin, stress for a given amount of displacement is lowered exponentially or linearly so that the structure of the movable table 303 connected through the support springs 304 has a degree of freedom with respect to movement in an X axis direction in the drawings, which is the width direction of the long edge 304a. As shown in FIG. 9, in the case where the width of the support spring is a and the thickness is b, an aspect ratio (b/a) is set to at least 1 and twisting displacement is suppressed when the movable table 303 is moved.
When this piezoelectric actuator 300 is moved in the X axis direction, a fixed voltage is applied to the stacked piezoelectric elements 306a for X direction movement to cause displacement. If the stacked piezoelectric elements 306a are displaced in the thickness direction, the movable table 303 connected by the guide sections 305a is joined and moves in the X direction. At this time, support springs 304 formed on the X direction edges move in the direction of the short edge. Also, X direction guide sections 305a function to guide the movable table 303 in the X direction. On the other hand, support springs 304 formed on the Y direction edges have difficulty moving in the direction of the long edge and so it is difficult to absorb displacement of the stacked piezoelectric elements 306a. The same also applies to movement in the Y direction.
However, with the above described piezoelectric actuator 300 of the related art, since stacked piezoelectric elements 306 are generally used it is necessary to first of all form the stacked piezoelectric elements 306 so as to satisfy relevant standards. The stacked piezoelectric elements 306 are generally manufactured using a green sheet method employing a green sheet made from a piezoelectric slurry. After conductive paste for internal electrodes has been screen printed on green sheets, a specified number of the green sheets are laminated and baked. Characteristics of a stacked piezoelectric element formed in this way are that strong generated force is obtained, but displacement is microscopic. The thus formed stacked piezoelectric element is fitted between a guide section 305 and a fixed table 301, and joining and complicated adjustment steps are necessary. This means that the manufacture of the XY stage for movement and the piezoelectric actuator 300 are difficult and complicated, and with increased amount of movement of the movable table 303 it is necessary to provide support points between the guide sections 305 and the fixed table 301 and to provided an enlarged cantilever. As a result, a correspondingly complicated structure results from further structural miniaturization.
The present invention has been conceived in view of the above described problems in the related art, and its object is to provide a novel approach to the problems.
In order to achieve this object, a piezoelectric actuator of a first aspect of the present invention comprises a base, a flat moving body constituting a cantilever with one end free and another end fixed and provided with piezoelectric elements, and support springs for supporting the moving body so as to track a surface of the base and for regulating direction of movement of the moving body.
If a alternating voltage is applied to the piezoelectric elements provided on the flat cantilever, the cantilever bends with oscillation and a free end of the cantilever comes into contact with the base. The free end of the cantilever undergoes elliptical motion which means that a sideways direction component excites movement of the moving body. Also, the contact state between the moving body and the base is kept stable by the support springs and the moving direction of the moving body is limited by the structure of the support springs, which means that motion and positioning of the moving body can be carried out easily.
A piezoelectric actuator of a second aspect of the present invention comprises a base, a flat moving body comprising a long-edged portion on which piezoelectric elements are provided and a short-edged section, and constituting a cantilever having the long-edged section free and the short-edged section fixed, and support springs for supporting the moving body so as to track a surface of the base and for regulating direction of move; of the moving body.
If the cantilever is formed having a long-edged section and a short-edged section, twisting vibration is excited at the same time as the cantilever bends with oscillation. As a result, the amplitude of oscillation at the free end becomes large and it is easy to obtain a larger motion of the moving body compared to the first piezoelectric actuator structure described above.
A third aspect of the present invention is the piezoelectric actuator of either the first or second aspects in which pressurization means is provided for causing the base and the moving body to be pressed into contact with each other. By pressing the moving body and the base with the pressurization means, not only is following further improved, and the state of contact with the cantilever made good, but also motion and locating of the moving body are made more stable.